摘要:

Abstract31P NMR spectra obtainedin vivoreveal the presence of a few reasonably well defined chemical species, namely, ATP, orthophosphate (Pi), and, in brain, phosphocreatine. The chemical shifts of these resonances respond to changes in concentrations of ions such as H+and Mg2+in a manner that depends on both the chemical shifts intrinsic to individual complexes and the formation or binding constants for the several complexes. Values of the appropriate formation constants are well established in the literature. We have derived estimates of the chemical shifts intrinsic to the individual complexes by analyzing high resolution spectra of solutions whose composition brackets the domain of physiological relevance. This provides information sufficient to estimate intracellular concentrations of H+and Mg2+from chemical shifts seen within vivospectra. The primary finding is an estimate of 0.3 mMfor the concentration of free magnesium in human brain. Differing values are obtained from other tissues.

ISSN:0952-3480    

DOI:10.1002/nbm.1940050202

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

Abstract1H spectra of tumours or normal tissues, which include signals from all hydrogen‐containing metabolites, are too complex for the human eye to interpret. We have studied 581H spectra from perchloric acid extracts of three normal tissues (liver, kidney and spleen) and five rat tumours (GH3 pituitary, fibrosarcoma, Morris Hepatomas 7777 and 9618a and Walker carcinosarcoma). Instead of editing them or quantifying individual metabolites, we have used statistical pattern recognition techniques to classify them into groups. This automatic, objective method differentiated spectra from normal and malignant rat tissue biopsies, and from different types of cancer. It seems likely that this technique can be applied to human tissues and thus used for cancer diagnosi

ISSN:0952-3480    

DOI:10.1002/nbm.1940050203

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractMeasuring theT1of the fluorine resonances of perfluorocarbons (PFC) is a unique method for monitoring oxygen tensionin vivo.However, because T1is also temperature sensitive, error in thepO2determination due to animal‐to‐animal temperature variation may arise. Pathophysiologic conditions, such as ischemia, where temperature is not known a priori may also introduce error. Thus, measuring the PFC temperature is clearly desirable in order to correct for tissue temperature variations during thepO2determination. Because the fluorine chemical shift of various fluorinated compounds has a significant temperature dependence, we evaluated the effect of temperature on the chemical shift of the fluorine resonances of perfluorotributylamine (FTBA). A linear relationship was found between chemical shift and temperaturein vitro. In addition, the relative FTBA chemical shifts were essentially independent ofpO2. Chemical shift temperature measurementsin vivo, obtained from a 10 μL FTBA bubble in the preretinal vitreous space of the rabbit eye, were in good agreement (±0.5 °C) with thermocouple measurements from the same location. Good agreement between the NMR determined temperature and core body temperature was also found. The implication of such temperature measurements for the ultimate accuracy of thepO2determination based on PFC T1measurements is discussed. To the best of our knowledge, this report describes the first absolute temperature measurementin vivo

ISSN:0952-3480    

DOI:10.1002/nbm.1940050204

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractOne‐ and two‐dimensional1H NMR spectra were obtained for normal murine thymus and malignant lymphoma tissue, as well as for the supernatant fractions from high speed centrifugal separations. Crosspeaks in the two‐dimensional spectra resembled those reported by others for adenocarcinoma and leukemic lymphoblast cells, assigned tentatively to the carbohydrate fucose. However, for the present systems, spectral analysis and the spectral response to addition of known compounds led to assignment of the crosspeaks as follows: 1.33–4.12 ppm, lactate anion; 1.33–4.26 ppm, threonine; 1.48–3.78 ppm, alanine. Differences between the NMR data for the normal and malignant specimens were only in the relative intensities of the peaks. No peaks characteristic of fucose were found in spectra of cytosol, tissue or membrane lipids. Thus, the NMR data for malignant lymphoma cells are significantly different from those for adenocarcinoma and leukemic lymphoblasts. The NMR characteristics of different types of cancer cell must be individually

ISSN:0952-3480    

DOI:10.1002/nbm.1940050205

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractSeveral multiple quantum editing techniques forin vivoproton NMR are discussed and compared using simulated and experimental data. Extensions of these techniques for improved editing are given. Relative S/N ratios, modulation characteristics, metabolite selectivity,B0andB1inhomogeneity and motion effects are considered. Frequency selective read pulses can be used for signal enhancement and lipid suppression. Extra suppression of undesired signals can be obtained with a two‐shot t1cycle which gives good results for both the zero and double quantum sequences. These sequences give at most 50% signal intensity and lipid suppression factors of ca 2000 and 7000, respectively. A sequence which selects zero and double quantum coherences yields 100% signal intensity but only gives a good lipid suppression factor (7000) in combination with phase cycling. It is shown that the multiple quantum modulation can be used to obtain specific metabolite editing. Corrections can be made for the effects of B0inhomogeneity on the multiple quantum coherences; B1inhomogeneity affects the investigated multiple quantum sequences in about the same way and decreases the volume of interest.In vivomeasurements show the good performance of the proposed zero and double quantum sequences for lactat

ISSN:0952-3480    

DOI:10.1002/nbm.1940050206

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA technique is reported for generating the quantitative area under selected peaks within a31P NMR spectrum. A numerical iterative method generates the fitted curve so as to minimize the RMS deviation between the fit and the experimental data. The curve is constructed from elemental grains of spectral density (“spexels”), each of which represents an elemental Lorentzian distribution, where the centre frequency and line width of the spexel may be varied within predetermined limits. This provides a fit that in principle is not restricted to a Lorentzian model. The method allows peak areas to be estimated, including the case of overlapping peaks. The method has been tested using simulated spectra containing six overlapping spectral lines each of known amplitude (ranging from 367 to 661 mV) and area; together with additional Gaussian noise with a standard deviation ranging from 30 to 646 mV. The results of fitting both unfiltered and filtered spectra were compared. The variation of quality of fit with spectral noise and filtering has been evaluated. In all cases, the method fitted the peak amplitudes to within 1% of the simulated value. The optimization processes provide an excellent non‐linear spectrum filtering algorithm. Provided the noise in the spectra did not exceed ca 400 mV, prefiltered data could be adequately f

ISSN:0952-3480    

DOI:10.1002/nbm.1940050207

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA technique for obtaining T1values from well localized regions using surface coils and with a clinically practicable measurement time is described. The method uses a two‐point Inversion‐Recovery/Saturation‐Recovery (IR/SR) sequence in conjunction with the image‐selectedin vivospectroscopy localization scheme. T1values are obtained by comparing the ratio of peak areas with those in a pre‐computed look‐up table. The method was tested by measuring the T1s of six calibrated water phantoms doped with different concentrations of gadolinium. This indicated an accuracy of 3% for T1values in the range 400‐1500 ms.31P spectra and T1values of Pi, phosphocreatine and α‐, β‐ and γ‐NTP metabolites from the calf muscle of healthy volunteers were obtained with the sequence employing Bi‐insensitive excitation pulses and a surface coil. The T1values fall within the range of published values obta

ISSN:0952-3480    

DOI:10.1002/nbm.1940050208

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe elimination and metabolism of enflurane, a fluorinated ether anaesthetic, was studied by19F NMRin vivoin both rat liver and brain as well as human body fluids. In the liver of thiobarbitone‐anaesthetized rats the half‐life for enflurane following exposure to 0.15% (v/v) for 30 min was 76 min but this could be decreased to 39 min by pretreatment of the animals with isoniazid (0.1% in the drinking water for 7 days), an agent known to enhance enflurane metabolism. In these animals the major organic metabolite difluoromethoxy difluoroacetate (DFMDFA) was also detected by19F NMRin vivo. This metabolite was detected along with fluoride ion in rat and human urine and plasma by high resolution19F NMR. Human urine also contained signals from a probable DFMDFA conjugate and unexpectedly from trifluoroacet

ISSN:0952-3480    

DOI:10.1002/nbm.1940050209

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

ISSN:0952-3480    

DOI:10.1002/nbm.1940050210

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY